occasional smoke from 86 740 turbo

I would be inclined to give the inlet tract a thorough cleanout including turbo hoses and intercooler if fitted. The Positive Crankcase Ventilation system could also do with a thorough clean (no filter in "Y" piece on turbo cars). I would guess at a bit too much oil residue slopping around in the turbo hosing/intercooler. The cleaning exercises should be done bi-annually.

All the best, Peter.

My guess: Valve seals...I would just try to live with it...

i believe you should not. check out your intercooler

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Steve wrote:

Hi,

You should check and clean all induction system hoses, then pcv stuff. If none of this stuff works, then before I gutted the engine, I would try an engine seal conditioning additive or oil, ie. Seafoam, or Valvoline Max Life synthetic (respectively). These things have additives that recondition, and sorta swell gaskets and seals. If this clears it up, great. I would use its efficacy as more of a diagnostic than a fix, but it may work for a while if seal damage is the culprit.

Best o' luck,

-Z-

I agree with Peter - clouds of blue smoke at idle in one of these beasts (I have an '85 765T) is a good indicator of crankcase ventilation trouble. Why it shows up mainly at idle isn't clear, but that's been my experience. In any event, back pressure causes the oil to back up into the turbo and spill into the exhaust - yuck!

Pull off all the pieces of the ventilation system: the hose that runs across the top of the engine, the plastic "Y" and the oil/air separator box under the intake manifold (it's held to the crankcase by two screws). Clean them up and check for restrictions, especially the separator box. Blowing through each should feel like you are blowing through a 3/8 inch hose; you should be able to exhale in 3 seconds or so. The separator box is more practical to replace than to clean if it's plugged. In my case even the large hoses were nearly plugged.

Don't forget to wipe the black ring off your lips after each restriction test!

Mike

My wifes car did this too ,much to our embarrassment at times .It sure was smoky but not all the time turned out the oxygen sensor was gone new sensor and all is fine as well as better fuel economy at $1.40.9 a litre we sure are need to keep it well tuned .